ac_sys_largefile_sensitive

checker whether the current system is sensitive to -Ddefines making off_t having different types/sizes. Automatically define a config.h symbol LARGEFILE_SENSITIVE if that is the case, otherwise leave everything as is.

This macro builds on top of AC_SYS_LARGEFILE to detect whether special options are neede to make the code use 64bit off_t - in many setups this will also make the code use 64bit off_t immediatly.

The common use of a LARGEFILE_SENSITIVE config.h-define is to rename exported functions, usually adding a 64 to the original function name. Such renamings are only needed on systems being both (a) 32bit off_t by default and (b) implementing large.file extensions (as for unix98).

a renaming section could look like this:
  #if defined LARGEFILE_SENSITIVE && _FILE_OFFSET_BITS+0 == 64
  #define zzip_open zzip_open64
  #define zzip_seek zzip_seek64
  #endif

for libraries, it is best to take advantage of the prefix-config.h macro, otherwise you want to export a renamed LARGEFILE_SENSITIVE in an installed header file. -> see AX_PREFIX_CONFIG_H

AC_DEFUN([AC_SYS_LARGEFILE_SENSITIVE],[dnl
AC_REQUIRE([AC_SYS_LARGEFILE])dnl
# we know about some internals of ac_sys_largefile here...
AC_MSG_CHECKING(whether system differentiates 64bit off_t by defines)
ac_cv_sys_largefile_sensitive="no"
if test ".$ac_cv_sys_file_offset_bits$ac_cv_sys_large_files" != ".nono"
then ac_cv_sys_largefile_sensitive="yes" 
  AC_DEFINE(LARGEFILE_SENSITIVE, 1,
  [whether the system defaults to 32bit off_t but can do 64bit when requested])
fi
AC_MSG_RESULT([$ac_cv_sys_largefile_sensitive])
])